Locking differential



April 11, 1961 A. o. ROBERTS 2,978,929

LOCKING DIFFERENTIAL Filed Jan. 12. 1959 2 Sheets-Sheet l lag INVEN TOR. 'F 7g 6 54 Azsmr 0 2055275 April 11, 1961 A. o. ROBERTS LOCKING DIFFERENTIAL I Filed Jan. 12, 1959 2 Sheets-Sheet 2 INVENTOR. ALBERT 0. POBERTQ BY SMITH, W/L90U, LEW/6 {was torque to the wheel having the greatesttraction.

3 A athc q iss b my tioniisf p e. e bye 7 .draulic device driven by rotation at the differential: gears t am as. a at LO'CKING DIFFERENTIAL Albert 0. Roberts, 116B Latta Road, Rte. 2, Durham, NC, assignor of forty percent *to'Arthur M. Smith, fDearborn, Mich. a

Filed Jan. 12, 1959, Ser. No. 786,159

6 Claims. (Cl. 74-711) This invention relates to difl erentials operable upon'the' attainment of a predetermined difference in speed between the driving wheels of a vehicle toinodify the torque dlVlding action of the difierential to drive both wheels, maintaining substantially the same difference in speed to exert the major portion of the. available torque on the wheel which has good traction.

Differential gearing is employed. between the driving axles of vehicles to divide the torque received from a driving source and to exert substantially equal torque on spaced driving wheels. Difficulties have heretofore been encountered in the operation of vehicles where one of the driving wheels has poor traction as when it is on ice or in mud where the traction available to that wheel is ma-' terially less than the traction available to the other wheel,

and the wheel having the poortraction therefore spins.

The differential functions to divide the torque equally between the driving wheels, and when one wheel starts to United States PatentO 2,978,929 Patented Apr. 11, 1961 ing force to relative rotation between the gears and case to transmit the available torque to drive the wheels substantially in proportion to variations in speed between the driving wheels.

A further object of my invention is to provide a controlled differential which functions after the attainment of a substantially predetermined diiference in speed of the driving wheels to drive the Wheels at a predetermined speed. ratio relative to each other regardless of the deoperative to resist further increase in differential speed.

spin no greater torque can be imparted to the wheel having good traction than to the wheel having poor traction, and which therefore is spinning. When the traction of one of the driving wheels has thus been lost, neither Wheel can eifectively drive the vehicle which is therefore stuck.

Many attempts have'been made to overcome these difiiculties. These prior efforts have been directed primarily to-the use of friction devices which function to vary the torque applied to the wheel which has the least traction to resist its rotation in an eiiort to impart greater torque to the wheel having good traction. Such devices are ineificient' and cause erratic steering and other undesirable actionin the control of the vehicle.

I have observed that when rounding curves, even the .Still another object of my invention resides in the provision of a compact speed controlled hydraulically actuated. differential which can be installed in standard axles Without substantial redesign or retooling, and wherein a desired speed ratio is maintained between the driving wheels.

Yet a further object of this invention is to provide a controlled differential which utilizes many standard parts of conventional differentials, and which thus provides a low-cost speed controlled diflierential to prevent spinning of one driving Wheel relative to another.

Another object is to provide a speed controlled differential mechanism which may be applied to difierentials of the bevel gear or spur gear types, and which functions to maintain the speedof rotation of the driving'wheels within desired predetermined speed ratios relative to each other.

A further object of my invention resides in the provision of a light-weight combinedhydraulic-mechanical differentialcontrolling device which functions to maintain a desired speed ratio between spaced driving wheels.

Still another object of my invention is to provide an improved locking differential which may be manufactured economically and which functions to prevent uncontrolled spinning of oneof the driving wheels relative to the other driving wheel.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this 7 specification wherein like reference characters designate most severe curves which can be negotiated in the driving it ing action ofthe differential until the difference in the speed of rotation of the driving wheels is approximately 20 rpm. When that difference in speedis approached my improved device becomes operative and exerts a progressively increasing retarding force on the spinning Wheel as the difference in speed between thedriving wheels increases. i J f 1 An object'of my invention is therefore to provide an hydraulic means for limiting the difference injspeed between the .driving wheels.

Another. objectfof myinvention is to provide speed controlled. hydraulically actuated devioefto prevent uncontrolled spinning of one of the driving wheels {thereby o app s insuringthe transmission of a large portion of thee 1? a n corresponding parts in the several views.

Fig. 1 is a longitudinal sectional view of a bevel gear type differential embodying my invention.

Fig. 2 is a sectional view taken substantiallyon the line 22 of Figs. 1 or 6 looking in the direction of the arrows.

Fig. 3 is an enlarged fragmentary view of a portion of one of the hydraulically restrained plungers illustrated in Figs. land 2. i

Figs. 4 and 5 are sectional views taken substantially on the lines 4 4 and 5-5 respectively of Fig. 1 looking in the direction of the arrows.

Fig. 6 is a longitudinal sectional view of the splngear type differential embodying my invention.

Figs. 7, 8 and9 are sectional views taken substantially looking in the directionof thearrows.

Before explaining thepresent invention in detail, it. is 510 be understood that the invention is notlin tited in its application to the details of construction and arrangement of parts illustrated infthe accompanying drawings,.since ,theinvention is capable oflother, embodiments and of being practi cecl.orcarried out'in .variousways. Also, it i Paa tast stfiat th lahteeglq v r g ammar.

contoured outer surface 60-of'the cam 28.

Anaanniilargrooveflfornredin the difierential case 3 employed herein is for the purpose of description and not of limitation.

Referring now more particularly to Fig. 1, my invention is illustrated as applied to a vehicle differential having' a ring gear-- p'rovided with angularly inclinedrgear' teeth 12 adapted to be engaged and'driven by apinion gear driven by a propeller shaft having a universal joint, not shown. The ring gear 10is secured to a rotatable assembly consisting of a differential case 14 and a differ-' ential case-cover 16 by means of, screws 18 projecting interconnects the apertures 70, a check valve 72. being.

interposed between each of the apertures 70 and the annular groove 71 to permit theflow of oil into the radial bores 54 but to prevent the reverse flow of oil therefrom.

As shown in Fig. 4 the annular groove 71 may be supplied with fluid such for example as oil through a plurality of axially extending drilled holes 74 inthe case 14 connected with a plurality of circumferentially spaced drilled holes 76 communicating through a screen 78 with the spacetiO within the dilferentialjcase 14 and cover 16.

Fluid may be supplied to the space 80from any convenient source. In the embodiment illustrated a selfcontained unit is provided wherein fluid is supplied ion shaft 20 is provided with differential pinions 22' of t the bevel gear type adapted to mesh with and drive differential side gears 24 and 26, also of the bevel gear type.

A multi-lobed cam 28, such for example as a six lobed cam illustrated more clearly in Fig. 2, is mounted for example adjacent the left-hand differential side gear 26, and has a hub 30 journalled in the bearing seat 32 carried by the differential case cover 16.

The right-hand differential side gear 24 has internal splines 34 which engage the splined inner end of an axle shaft 36 to which a driving wheel is attached. The outer. end of the differential case 14 is provided with a bearing seat 38 adapted tov receive a suitable bearing by which the right-'hand end of the differential case 14 is journalled within an axle carrier 40.

The left-hand differential side gear 26 is provided with internal splines 42, and the multi-lobed cam 28 has similar internal splines 44to receive the inner splined end of an axle shaft 46 to which the other driving wheel is secured. It will be noted that hearing seat 32 carried by the differential case-cover'16 also receives a suitable bearing to. journal the left-hand end of the case assembly 1416 in the axle carrier 40. It will of course be apparent that if desired the cam member 28 may be formed integrally with the left-hand side gear 26.

The differential case-cover 16 is provided with a plu- V rality of radial cylindricalbores 54 as more clearly shown in Figs. 1 and 2. Each of the radial bores 54 isprovided with a radially movable plunger 56 having a rounded inner-end or contoured nose 58 to engage in linecontact,

theouter contoured surfaces or lobes 60 of the cam 28. The plungers 56 have: hollow interiors to receive springs 62 which yieldingly urge the plungers radially inwardly in thev bores 54 to maintain contact between the inner ends 58 of the plungers 56 and. the contoured surfaces or lobes 60 of. the cam 28. The inner ends of the plungers 56, are provided with check valves 64, more clearly shown in Fig. 3, and having calibrated orifices 66' to permit a controlled flow offluid radially inwardly ing 67 to serve as a check valve'to prevent the intake of V vehicle rounds the tightest curve over'which it can be air- .from the space between the cover 16 and the contoured surface of the camv 28. p

'The springs 62 which hold theplnnge rs 56 in contact with the cam are held in place byrretainingplugs 68 threaded in the outer ends of the radial bores 54; The springs 62 may be'calibrated to exert a desiredinward thrust on the plungers -56 {to maintain the rounded inner ends 58 of the plungers at all times'in-contactwith'the mid under light P s s pplied to eac br ttle plunger receiving "radialbores 54 throughiapertnres?70' I through a radial groove 82 formed in the differential case 14, for example adjacent the" right-hand differential side gear 24. The radial groove-82 communicates with an axially extending bore 84 connected with an annular circumferential groove .86'formed in' the case 14; Fluid under pressure may besupplied to the annular groove-86' through a check valve 88 from a space 90 in a pump formed by an oscillating cylinder 92 carriedby a yoke 94 mounted on an eccentric portion 96 of the hub on the differential case 14. A piston 98. is pivotally supported on a pin 102 secured in a stationary stud 104 in the axle carrier 40. for reciprocal movement'in the cylinder 92 slidably mounted thereon.

housing to form a fluid reservoir in a'known-manner.

I have illustrated my invention as applied to a construction wherein tenradially movable plungers56' carried by, the case and cover assembly 1416 are slidably mounted in the circumferentially spaced radial bores 54, the inner ends 58 of the plungers 56 being maintained in contact with the contoured surfaces or lobes 60 of the multi-lobed cam 28. The cam 28 andthe left-hand side gear 26 are splined to the axle shaft '46 and therefore 3 I of; the plungers. 56 permit a sufficient flow of fluid through the plungers 56, to accommodate a differential of rotadriven.

It will. thus be appreciated that during all normal op- "erations of the vehicle my improved differential functions asdoes a standard differential and it will be apparent that no interference to the drive is interposed,

The operation is as follows. While the vehicle in which my improved differential is mounted is driving straight ahead,:there is no relative rotational movement between the cam 28 splined to theshaft 46 and the differential case and cover'assembly 14-165 The plungers'56are at all times maintained in contact with the lobes 60 of the i cam 28 by the springs" 6-2,"an'd oil under 'light' pressure,

suppliedfromthe pump formedby the cylinder 92 and the 'piston 98, is maintained in the radial bores 54'an'd the outer ends of the plungers 56. The calibrated orifices 66 in thelinner ends of the plungers 56'permit the I escape of asufficient quantityofoil from the bores 34 through th'e plungers 56 to permit' slow.rotationfof the. J

I ca'my28 and, the axle shaft 46' relative. to thef case. and cover asseinbly"14-.-'- 16 to permit relative rotatioriiof urve about whiehthevehiele canbedrive When; one of. the driving wheelslo A check valve 106 is interposed between the'space 90 and a bore 108 in the piston 98 communicating through an aperture 110 with the lubricant inthe axle carrier 40 which cooperates with an axle a will begin to spin. This results in increased relative rotational'movement between the. cam 28 and the casingcover assembly 14-16 whereupon fluid under pressure is trapped in the radialbores 54 at the outer ends of the plungers 56. The calibrated orifices 66 will not permit the escape of fluid at a sufficiently high rate to accommodate the increased rotational speed between the shaft 46 and the cover and case assembly 14-16. When one wheel tends to rotate faster than the other by an amount greater than the approximate 20 rpm. the fluid is not permitted to escape through the orifices 66 sufficiently rapidly andfluid is therefore trapped in the bores 54 at the outer ends of the plungers 56 to resist outward movement of the plungers 56 in the bores 54. The lobes 60 of the cam 28 carried by the shaft 46 must shift the plungers 56 outwardly in the bores 54 formed in the case and cover assembly 14-16 to permit rotational movement of the shafts 36 and 46 relative to the casingcover assembly 14-16. The fluid trapped in the bores 54 at the outer ends of the plungers 56 resist greater rotational speed of the shafts relative to the casing than is permitted by the calibrated orifices 66. The plungers 56 thus exert a braking force on the cam 28 which resists increased rotational movement of the shafts relative to the case. The shafts 36 and 46 being tied together through the gearing are both forced to rotate together at a speed dependent on the quantity of fluid forced through the orifices 66 in the plungers 56. The wheel having good traction must therefore rotate in order to permit the other wheelwhich has lost its traction to rotate. The vehicle Wheels lose will therefore not becomestuck unless both their traction. I

Described another way it'will be apparent that during straight ahead driving of the vehicle the axle shafts 36 r and 46 rotate in the same direction and at the same speed,

and there is no relative rotation between the case-cover assembly 14-16 and either of the axle shafts 36-46. When the vehicle rounds a curve the wheel on the outside of the curve travels a greater distance than does the Wheel on the inside of the curve. To accommodate this difference in distance traveled the axle shafts 36 and 46 rotate relative to each other. The rotatable assembly consisting of the case-cover members 14-16 continues to be driven at the speed dictated by the drive shaft,

and the axle shafts 36-46 rotate at appropriate speeds -to accommodate the distance being traveled by their respective driving wheels. There is thus relative rotational movement between the relatively movable members consisting of the case-cover assembly 14-16 and the cam member 28 splined to the axle shaft 46. This rotation causes thefplungers 56 to reciprocate in their cylindrical bores 54. The plungers areforced radially inwardly by means ofthe springs 62, andfthey are forced radially outward by the cam 28. The inward movement of the plungers draws oil in through check valves 72, the check valves 64preventing the intake of air which would reduce the efficiency of the device. The outward movement of the plungers 56 compresses oil in cylindrical bores .54

forcing itthrough orifices 66, check valves 72 at the outer ends of the bores 54 having closed. The resistance to flowfof fluid throughthe orifices 66 controls the outward speed of movement of the plungers 56 thereby offering a resistancf'e to increase in the speed of rotation of the cam 28 carried by the shaft 46.

The.fight-handfaxle shaft 36 being connected "to the case-cover assembly 14-16 through the side gear 24 and thepiniongears 22 is prevented from spinning relative to theaxle shaft. 46. The torque from the prime mover is thus exerted on the wheel having good traction whereupon the danger. of the vehicle becoming stuck is "overcome, provided one of thedrivingwheels has good traction. The action of the .cam is the same regardless of the direction .of its rotation therefore the effect in controlling onedrivingwheel is the same as the effect on the other.

It will be apparent that if desired suitable relief valves can be employed to limit the maximum pressure which.

can be exerted in the bores 54 resisting outward movement of the the axle.

The embodiment illustrated in Figs. 6 to 9 is similar .in many respects to that illustrated in Figs. 1 to 5. It will be noted that the ring gear 12 is secured to a rotatable assembly consisting of a case member 120 and a casecover 122 by the screws 18. As shown in Fig. 7 the case member 120 has a plurality, five in the embodiment illustrated, of circumferentially spaced gear pockets 124 which receive spur gears 126 in rotating relation therein.

The gears 126 substantially fill the gear pockets 124, running clearance being provided between the outer peripheries of the gears 126 and the internal walls of the case 120 defining the pockets 124 so that it is unnecessary to employ hearings to support the gear members 126. As shown in the lower portion of Fig. 6 the gears 126 mesh with a side spur gear 128 splined to the axle shaft 36.

In like manner, as illustrated in Fig. 8, the cover assembly 122 of the case 120 is provided with a corresponding number of correspondingly spaced gear pockets 1 30 which receive a corresponding number of spur gears 132 which mesh at their inner peripheries with a side spur gear 134 splined to the left-hand axle shaft 46. Gears 132 and 126 are identical and gears 134 and 128 are identical.

' As best shown in Fig. 6 it will be noted that the spur gears 126 positioned in the pockets 124 formed in the case 120, and the spur gears 132 positioned in the pockets 130 of the cover 122 are longer axially than the depth of their respective pockets 124 and 130. The pockets 124 and 130 in the case and cover members 120 and 122 are;

i spaced. circumferentially, as illustrated in Figs. 7 to 9, so.

that when assembled in the pockets the spur gears 126. and 132 overlap axially and mesh with each other as. shown at 136 in'Figs. 6 and9. The pinion gears 126 carried by thecase member mesh with their respective side gear 128, and the pinion gears 132 carried by the cover 122 mesh with their side gear 134. The confronting ends of the side gears 128 and 134 are cut away at their outer peripheries as illustrated at 138 and 140 respectively, to prevent meshing engagement with the pinion gears 126 and 132 of the case and cover members 120 and 122 respectively.

The cam 28 is splined to the axle shaft 46 in the same manner as described in connection with the embodiment illustrated in Figs. 1 to 5, and-the plungers 56 are slidably mounted in the circumferentially spaced radially extendrotates. When the vehicle is proceeding straight ahead. the axle shafts 36 and 46 are driven in the same direction and at the same speeds as the case and cover assembly 120-122 and the ring gear 12 as previously described in connection with the Figs. 1 to 5 embodiment. When the vehicle rounds a curve, the wheel on the outside of the curve travels farther and therefore the wheel on that side rotates faster. For example, let it be assumed that a turn is being made to the left whereupon the axle shaft 36 will rotate faster than will the axle shaft-16; The

'rotatable assembly consisting of the case 120 and the cover 122then rotates relative tothe axle shafts 36fand 46.. The speed of thecase 120 and cover 122 being less than the speed of rotation of the axle shaft 36 and greater than the speed ofrotationof the axle shaft 46.

The spur pinions 12'6 carried by the casingmember 120 rotate in their respective pockets 124 and drive the side gear 128 at a faster speed to accommodate the increased distance over travel.

In like manner the spur pinions l3 2carriedin the pockets of the case cover 122 rotate in the opposite 1 plungers 56 to avoid overloading any part of which, the right-hand wheel must connection with the Figs. 1 to 5 embodiment;

direction from the pinions 126 to drive the side gear 134 and left-hand axle shaft 46 at a lower rate of speed than the'd'rive of the right-hand side gear 128 and the axle shaft-36. The fact that, as shown in Fig. 9, the pinion gears 126: of the case 120 mesh with the gears 132 journalled in the cover 122 insures that the side gears 128 and 134 splined to the axle shafts 36 and 46 respectively rotate in opposite directions relative to the rotation of the case and cover assembly 120-122. Since these pinions 126 and l32 have no bearings and are supported only on their peripheries within-the gear pockets 124 and 13tl the separating force between the gears due to tooth pressure angle applies a load between the periphe'ries of the gearsand the internal surfaces of the gear pockets so that a frictional resistance load is applied to resist rotation of the differential gears. This frictional resistance varies with the torque applied so that at low torque, the resistance to the differentiating function is negligible. 'Also the axle shaft torque acting through side gears 128 andl34 imposes a load between pinion gears l32'and 126 and their respective pockets-130 and 124 and this force is added vectorially to the abovementioned separating force. As the speed of'rotation between the side gears 128 and13-4 increases the force resisting the spinning of one of the side gears 36 and 46 relative to each other increases At higher torques this thrust-load becomes considerable and therefore considerable resistance to dilierential action is set up. This reluctance to differentiate so introduced removes some of the load imposed on the hydraulic unit when one wheel encounters poor traction and attempts to spin. The

mechanical "resistance thus imposed to relative rotation between the shafts 36 and 46 is added to force resisting relativerotation-exerted by my improved hydraulic con trol.

The speed controlled hydraulic device for resisting spinning of one of the driving'wheels is thesame'in structure and mode of operation as that described'in The plungers 56 engaging-the cam 28 splined to the shaft 46 function to resist rotational movement of the shaft relative to the case in proportion to thelleakage'of fluid through the plungers 56 as previously described.

I have illustrated my invention in connection with a device wherein fluid, oil, is supplied to the space within the rotatable assembly consisting of the'case and cover members 1416 by the pump driven by rotation of the rotatable assembly lttwill of course be apparent that any desired fluid may be supplied to the cylindrical bores 54 from my desired source which need not be associated with the differentialbut cantbe supplied by any movable portion ofthe vehicle. 7 t t Y 1 While my invention has beenillustrated and described in connection with a device having a six lobed cam and a ten plunger braking structure to limit rotational movement'betwe'en the differential caseand the shafts, it will be apparent that thenurnber of lobes on the cam and the number "of plungers can be varied. The braking force exerted during'each revolution may be computed by multiplying the displacement 'of each plunger determined by multiplying the areaof the plunger by the displacement I ofrthelobes of the" cam," multiplied. by the number of V lobeson "the cam; and multiplying the resultantlby the number "of plungers employedx- Attention; is directed to the fact that by using a large number'oflobe'soh the cam and a large number of plungers'it is'possible-to embody a high restraining force in' a comparatively small area thereby adapting my invention for use in vehicle differentials withminim'um changes in structure.

, While' my' inve'ntion has been illustrated and described withparticular]reference to specific embodiments, it"willf be apparent that various changes may be made WithOllt departing froin the spirit of my' inventi'on'as' definedby the following claimsi' 1. In a fiuid type locking differential for use with a power source, the combination of, a differential carrier adapted to be positioned in an axle housing; a differential case rotatably positioned in said'carrier; a pair;of side gears and difierential pinion gears positioned in said differential case; a multi-lobed cam positioned adjacent one i of said side gears; a plurality of openings extending through said differential case in alignment with said multilobed earn; a piston positioned in each of said openings;

means for limiting travel of said pistons; each ofsaid" pistons having a restricted escape orifice therein; means for maintaining each of said pistons in contact'with said multi-lobed cam; and fluid supply means; the restricted escape orifices in each of said pistons to control the quantity of fluid discharged, thereby limiting the relative movement thereof.

2.1a a fluid type locking diflerential for use with a power source, the combination of, a ditferentialcarrier adapted to be positioned in an axle housing; a ditferential case rotatably positioned in said carrier; a pair ofsidc gears and differential pinion gears positioned in said differential case; a multi-lobed cam positioned adjacent one of said side gears; a plurality of radial openings extending through said differential case and in alignment with said circumferential end of said openings for limiting travel'of each of said pistons; fluid supply means; the calibrated orifices in each of said pistons controlling the quantity of fluid discharge, thereby limiting the relative rotation of the'cam; t

3. In a fluid actuated locking differential foruse with a power source,'the combination of, a differential carrier adapted to be positioned in'an axle housing; a two part differential case rotatably positioned in said carrier; a pair of side gears and differential pinion gears positioned in said'diflerential case; one side gear positioned in each part of said differential case; a multi-lobed cam positioned adjacentone of said side gears in one of said differential case parts; a plurality of cylindrical openings extending through said diflerential case and in perpendicular align- ,ment with said multi-lobed cam; a piston operatively posi tioned in each of said openings; each of said pistons having a calibrated orifice therein; means for maintaining each of said pistons in contact with said cam; means for limiting the travel of said piston; fluid supply means; the calibrated orifices in said piston controlling the quantity of fluid discharged, thereby limiting-the relative movement of the cam with respect'to the differential case.

4. Ina fluid type locking differential for use with a power source, the combination'of, a differentialcarrier adapted to be positioned in an axle housing; a two part differential case rotatably positioned in said carrier; a pair of side gears and differential pinion gears positioned in said differential case; one side gear positioned in each part of said differential case; a multi-lobed cam positioned adjacent one of said" side gears in one of said differential case parts; a plurality of cylindrical jopenings extending diametrically through said differential case, the central portions thereof terminating in perpendicular'alignment with said multielobed earn; a cylindrical piston positioned in each of-said openings; check valve-means in eachof" said pistons; each of said pistons having a calibrated orifice i I therein; yieldable means for vmaintaining each of said pistonsin contactwithsaid cam; means fior-rendering said cylindrical openings fluid tight and limiting the travel ofsaid pistons; fluidsu'pp'ly means; the calibrated orifices in 7 said "piston controlling the quantityof fiuididischarge'd, thereby limiting the relative rotationalmovementof the cam.

5'. in" a fluid actuatedlockingdifferential for use witha ppwer -s ource, the combination of, a diiferential'carrier'i adapted tob" positioned in an axle housing; a two-part differential case rotatably positioned in said carrier; a pair t of side gears and diflerential pinion gears positioned in said differential case; one side gear positioned in the first section of said differential case; one side gear positioned in the second section of said differential case; a multi-lobed cam positioned in contact with said side gears in said first section of said diflerential case; a plurality of cylindrical openings in said first section of said diflerential case extending diametrically through and in alignment with said multi-lobed cam; a piston positioned in each of said openings; check valve means in each of said pistons;'each of said pistons having a calibrated orifice therein; yieldable means for maintaining each of said pistons in contact with said cam; means for rendering said cylindrical openings fluid tight and for limiting the travel of said piston; fluid supply means; the calibrated orifices in said piston contro1- ling the quantity of fluid discharged, thereby limiting the relative rotational movement of the cam.

6. In a fluid actuated locking diflerential for use with a power source, the combination of, a difierential carrier adapted to be positioned in an axle housing; a differential case having body portion and cover member rotatably positioned in said carrier; a pair of axially disposed side gears and vertically disposed differential pinion gears positioned in toothed engagement in said difierential case; the

first side gear and two differential pinion gears positioned in said differential case body; a pocket in said cover member adapted to receive a multi-lobed cam; the second side gear in contact with the side of said cam; a plurality of radial openings extending through said diiferential case cover and in vertical alignment with said multi-lobed cam; a cylindrical piston positioned in each of said radial openings; each of said pistons having a calibrated orifice therein; yieldable means for maintaining each of said pistons in contact With said multilobed cam; stop means in the circumferential ends of said differential case cover for limiting travel of each of said pistons; fluid supply means; the calibrated openings in said piston controlling the quantity of fluid discharge, thereby limiting the relative rotation of the cam.

References Cited in the file of this patent UNITED STATES PATENTS 2,122,284 Heumader June 28, 1938 2,307,310 Ballarny July 9, 1940 2,397,374 Schlicksupp Mar. 26, 1945 2,722,140 Cabell Nov. 1, 1955 2,808,739 Mueller Oct. 8, 1957 

